A new study analyzed numerous research trials to determine the content of the supposedly "inactive" placebos used for research, but discovered that placebo disclosure is rare.
Researchers examined 176 medical journal studies and found that the vast majority didn't mention the contents of the placebos at all.
The study authors argued that placebo ingredients may be important. Certain placebos could skew results in favor of the active drug.
According to the Los Angeles Times:
"The researchers referenced a trial for a drug used to treat anorexia linked with cancer in which a lactose placebo was used. Since lactose intolerance is common among cancer patients, the fact that some suffered stomach problems from the placebo may have made the actual drug look more beneficial."